In the oil and gas industry wellbores are drilled from surface to intercept subterranean hydrocarbon bearing formations. It is known to extend completion equipment into a drilled wellbore to facilitate appropriate inflow of subterranean fluids and subsequent safe retrieval to surface. The completion equipment may include a production pipe string which carries a number of packers on an outer surface thereof such that when the packers are set multiple axially spaced and isolated production zones may be established. The production pipe string may include one or more inflow devices within each zone, to facilitate inflow of formation fluids. A basic form of inflow device includes a port in a wall of the production pipe string. However, other forms may include nozzles which can provide a desired fluid choking effect, Different zones may be fitted with inflow control nozzles or devices of different design, providing a variation in inflow restriction across different zones. This variation may be used to provide a more balanced production of formation fluids across the different zones, which might assist to provide more even hydrocarbon recovery and delay breakthrough of undesired fluids, such as water and gas.
In some instances an inflow control device may function as a valve, to selectively open and close in accordance with user preference and/or fluid properties. For example, Autonomous Inflow Control Devices (AICDs) are known which can permit the inflow of a liquid hydrocarbon, but automatically close or choke flow of water or a gas. Some AICD designs function on the basis of the changing fluid inflow velocity, which will be a function of the fluid viscosity and density.
It may be desirable in some wellbore operations to restrict or prevent backflow of a fluid from a production pipe string into a surrounding formation. Further, it may be desirable to restrict or prevent cross-flow of fluid from a higher pressure zone to a lower pressure zone.